uring World War II, bombs were dropped throughout Germany, the UK and other European countries. Many of these bombs failed to detonate and were buried in the ground. Now, more than 70 years later, these hidden threats – unexploded ordnance (UXO) – remain buried underneath urban centers and rural lands. Today, in Germany, it is estimated that there are still 100,000 unexploded and undiscovered bombs lurking in the ground. To ensure safety during construction projects, German legislation requires that the work site must be cleared of unexploded ordnance before the construction can begin.

Mapping magnetic fields over the area is the most common method for UXO detection since buried bombs are iron-rich metallic objects. This method works well in open areas outside of cities, but when working in urban areas with extensive metallic infrastructure (fences, vehicles, pipes, etc.) these other metallic objects create magnetic field disturbances that can mask a buried bomb response. In these cases, ground penetrating radar (GPR) becomes a useful alternative. GPR is less affected by nearby metallic objects and can be effectively used to pinpoint the position of objects buried in the ground.

GPR also provides an indication of the depth of buried objects, especially important in UXO detection. Once a UXO is detected, it has to be uncovered, defused and removed from the site. Having a precise depth to the UXO allows the removal teams to carefully excavate and remove the hazardous device.

One area that was subject to significant bombing during World War II was the airport in Oberschleissheim, north of Munich. Hundreds of bombs are still suspected to be buried in the airport compound. The company MuN Ortung GmbH was contracted to investigate a 10,000 m2 area of the airfield and safely remove all UXO (Figure 1).

Figure 1:

Aerial image of the airport in Oberschleissheim from 1945, with the UXO survey area overlaid in green.

As a first step, they scanned the area with their 7-channel magnetometer system, towed behind a vehicle to quickly gather data over the entire survey area. Upon completion of this survey, they collected lines with their Noggin 250 MHz SmartCart GPR system over the anomalies (Figure 2) to confirm the findings and determine the depth to the targets.

Figure 2:

Magnetic survey results indicating point targets of interest. GPR lines (2-6) were collected over the areas of interest to confirm findings and determine depth of the target.

The GPR data clearly shows the hyperbolic response of the buried targets, as well as the expected depth of the target. (Figure 3). Using the additional information from the GPR survey, they carefully began excavating the suspected UXO.

Figure 3:

Figure 3a GPR Line 2 was collected across a linear target (likely a utility pipe) anda point target. The GPR line data clearly shows the pipe at 1m depth and the suspected UXO buried just beneath the surface.Figure 3b GPR Line 3 shows a suspected UXO at a slightly deeper depth of 1m.

Figure 4:

Excavation revealed a shallow buried bomb corresponding to the target location and depth in the GPR Line 2 data.

At each anomaly, a type GP 150lb T1 (General Purpose) bomb was discovered. (Figure 4). Each bomb was carefully removed, defused, and set aside for disposal.

The UXO survey was successful, and 5 potentially deadly UXO (Figure 5) were safely located and removed thanks to the Noggin GPR system and the expertise of the MuN Ortung team.

Figure 5:

A total of 5 type GP 150lb T1 (General Purpose) bombs were located and safely excavated from the airport